U.S. patent number 6,981,370 [Application Number 10/308,969] was granted by the patent office on 2006-01-03 for method and apparatus for pm filter regeneration.
This patent grant is currently assigned to Caterpillar Inc. Invention is credited to Cornelius N. Opris, Maarten Verkiel.
United States Patent |
6,981,370 |
Opris , et al. |
January 3, 2006 |
Method and apparatus for PM filter regeneration
Abstract
A method and apparatus for initiating regeneration of a
particulate matter (PM) filter in an exhaust system in an internal
combustion engine. The method and apparatus includes determining a
change in pressure of exhaust gases passing through the PM filter,
and responsively varying an opening of an intake valve in fluid
communication with a combustion chamber.
Inventors: |
Opris; Cornelius N. (Peoria,
IL), Verkiel; Maarten (Metamora, IL) |
Assignee: |
Caterpillar Inc (Peoria,
IL)
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Family
ID: |
32392872 |
Appl.
No.: |
10/308,969 |
Filed: |
December 3, 2002 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20040103648 A1 |
Jun 3, 2004 |
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Current U.S.
Class: |
60/311; 60/295;
60/278; 60/274 |
Current CPC
Class: |
F01N
3/0231 (20130101); F01N 3/035 (20130101); F02B
37/004 (20130101); F02D 13/0269 (20130101); F02D
41/029 (20130101); F01N 9/002 (20130101); F02B
37/013 (20130101); F02D 41/0002 (20130101); Y02T
10/142 (20130101); Y02T 10/47 (20130101); F02M
26/23 (20160201); Y02T 10/12 (20130101); F02M
26/08 (20160201); F02D 41/0065 (20130101); F02D
2041/002 (20130101); Y02T 10/40 (20130101); Y02T
10/42 (20130101); F02D 2041/001 (20130101); Y02T
10/144 (20130101) |
Current International
Class: |
F01N
3/02 (20060101) |
Field of
Search: |
;60/274,278,295,297,311
;123/90.15 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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3-271515 |
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Dec 1991 |
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JP |
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409013951 |
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Jan 1997 |
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JP |
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Primary Examiner: Denion; Thomas
Assistant Examiner: Tran; Diem
Attorney, Agent or Firm: Finnegan, Henderson, Farabow,
Garrett & Dunner
Government Interests
This invention was made with government support under the terms of
DOE HTCD & LTCD programs, DOE Contract Nos. DE-FC05-00OR22806
& DE-FC05-97OR22605. The government may have certain rights in
this invention.
Claims
What is claimed is:
1. A method for initiating regeneration of a particulate matter
(PM) filter in an exhaust system in an internal combustion engine,
including the steps of: determining a change in pressure of exhaust
gases passing through the PM filter; and extending an open duration
of an intake valve in fluid communication with a combustion chamber
beyond a normal duratio in response to the change in pressure to
increase a temperature of the exhaust gases passing through the PM
filter.
2. A method, as set forth in claim 1, wherein extending an open
duration of an intake valve includes the step of extending an open
duration of the intake valve in response to the change in pressure
being greater than a predetermined threshold.
3. A method, as set forth in claim 1, wherein extending the open
duration beyond a normal duration includes the step of extending
the open duration into a portion of a compression stroke of the
internal combustion engine.
4. A method, as set forth in claim 1, further including the step of
returning the open duration of the intake valve to the normal
duration in response to the change in pressure being less than the
predetermined threshold.
5. A method, as set forth in claim 1, further including the step of
varying a throttle valve located in an intake passageway in
cooperation with varying the opening of the intake valve.
6. A method, as set forth in claim 1, wherein determining a change
in pressure includes the step of sensing a difference in pressure
of the exhaust gases passing through the PM filter.
7. A method, as set forth in claim 1, wherein determining a change
in pressure includes the step of estimating a change in pressure as
a function of at least one parameter associated with the internal
combustion engine.
8. A method, as set forth in claim 2, further including the step of
determining a flow of exhaust gases passing through the PM
filter.
9. A method, as set forth in claim 8, further including the step of
varying the opening of the intake valve in response to at least one
of the change in pressure and the change in flow of exhaust gases
being greater than the predetermined threshold.
10. A method for initiating regeneration of a particulate matter
(PM) filter in an EGR system in an internal combustion engine,
including the steps of: determining a change in pressure of exhaust
gases passing through the PM filter; and extending an open duration
of an intake valve in fluid communication with a combustion chamber
in response to the change in pressure being greater than a
predetermined threshold to reduce an amount of air available for
combustion.
11. A method, as set forth in claim 10, wherein extending the open
duration includes the step of extending the open duration into a
portion of a compression stroke of the internal combustion
engine.
12. A method, as set forth in claim 10, further including the step
of returning the open duration of the intake valve to a normal open
duration in response to the change in pressure being less than a
second predetermined threshold.
13. A method, as set forth in claim 12, further including the steps
of: controlling a throttle valve to reduce a flow of air through an
intake passageway in cooperation with the open duration of the
intake valve being extended; and returning the throttle valve to a
position to allow a normal flow of air through the intake
passageway in cooperation with the open duration of the intake
valve returning to the normal open duration.
14. An apparatus for initiating regeneration of a particulate
matter (PM) filter in an EGR system in an internal combustion
engine having a combustion chamber and an intake valve in fluid
communication thereof, comprising: means for determining a change
in pressure of exhaust gases passing through the PM filter; and a
controller for extending an open duration of the intake valve in
response to the change in pressure to increase a fuel to air
ratio.
15. An apparatus, as set forth in claim 14, further including: an
intake passageway located in fluid communication with the intake
valve; and a throttle valve located within the intake
passageway.
16. An apparatus, as set forth in claim 15, wherein the throttle
valve is actuated by the controller in cooperation with the
extended open duration of the intake valve.
17. An apparatus, as set forth in claim 14, wherein the means for
determining a change in pressure includes a pressure sensor.
18. An apparatus, as set forth in claim 14, further including means
for determining a flow of exhaust gases passing through the PM
filter.
19. An apparatus, as set forth in claim 18, wherein the means for
determining a flow of exhaust gases includes a flow sensor.
20. An apparatus, as set forth in claim 18, wherein the controller
is adapted to extend the open duration of the intake valve beyond a
normal open duration in response to determining at least one of the
change in pressure of the exhaust gases and the change in flow of
exhaust gases being greater than a predetermined threshold.
21. An apparatus, as set forth in claim 20, wherein the extended
open duration is a portion of a compression stroke of the internal
combustion engine.
22. An apparatus for initiating regeneration of a particulate
matter (PM) filter in an EGR system in an internal combustion
engine, comprising: a combustion chamber located in the engine; an
intake valve in fluid communication with the combustion chamber; a
variable intake valve closing mechanism configured to keep the
intake valve open by selective operation of the variable intake
valve closing mechanism; means for determining a change in pressure
of exhaust gases passing through the PM filter; and a controller
for actuating the variable intake valve closing mechanism to extend
the open duration of the intake valve in response to determining
the change in pressure being greater than a predetermined threshold
to increase a temperature of the gases passing through the PM
filter.
23. An apparatus, as set forth in claim 22, further including: an
intake passageway located in fluid communication with the intake
valve; and a throttle valve located within the intake passageway,
wherein the throttle valve is actuated by the controller in
cooperation with the extended open duration of the intake
valve.
24. An apparatus, as set forth in claim 22, wherein the means for
determining a change in pressure includes a pressure sensor.
25. An apparatus, as set forth in claim 22, further including means
for determining a flow of exhaust gases passing through the PM
filter.
26. An apparatus, as set forth in claim 25, wherein the means for
determining a flow of exhaust gases includes a flow sensor.
27. An apparatus, as set forth in claim 22, wherein the controller
is adapted to extend the open duration of the intake valve beyond a
normal open duration in response to determining at least one of the
pressure of the exhaust gases in the PM filter increasing above a
predetermined threshold and the flow of exhaust gases through the
PM filter decreasing below another predetermined threshold.
28. An apparatus, as set forth in claim 27, wherein the extended
open duration is a portion of a compression stroke of the internal
combustion engine.
Description
TECHNICAL FIELD
This invention relates generally to a method and apparatus for
regeneration of particulate matter (PM) filters and, more
particularly, to a method and apparatus for initiating regeneration
of PM filters by determining a change in pressure of exhaust gases
passing through a filter and changing operating conditions of an
internal combustion engine to increase exhaust temperature and
initiate regeneration.
BACKGROUND
Internal combustion engines perform a wide variety of useful tasks
and have become an integral part of technological society over the
years. Transportation and power generation needs have been met
largely due to advances in engine technology, and the use of
engines has become necessary for society to function.
The growth in the use of internal combustion engines, however, has
resulted in severe problems and issues, one of which is the degree
of pollutants being emitted by the ever-increasing number of
engines in use today. The rapid increase in the levels of NO.sub.x
and particulates, such as soot, has created the requirement for
stringent standards to be developed to reduce such emissions as
much as possible.
One method for reducing the amount of undesired pollutants is to
employ an exhaust gas recirculation (EGR) system in the exhaust
stream of an internal combustion engine to re-route exhaust gases
back through the engine for more complete combustion to take place,
thus lowering the amount of pollutants ultimately allowed to enter
the atmosphere. One aspect of EGR systems is to include particulate
matter (PM) filters, also known as PM traps, to filter out
particles in the exhaust stream.
PM filters work well, but must be "cleaned out", i.e., regenerated,
from time to time, as the particulate matter accumulates. A common
method for regenerating PM filters is to increase the temperature
within the filter, thus causing the accumulated matter to combust
and bum. The temperature increase may be done actively by the use
of heating elements installed in the filter, or may be done by
increasing the temperature of the exhaust gases passing through the
filter.
Several attempts have been made to control engine parameters to
increase exhaust temperature to initiate regeneration. For example,
in U.S. Pat. No. 6,304,815, Moraal et al. disclose a system which
controls a throttle valve at an intake manifold to increase
temperature for regeneration. In U.S. Pat. No. 6,196,183, Bauer et
al. disclose a system which varies injection time and ignition time
to initiate regeneration. In U.S. Pat. No. 6,173,571, Kaneko et al.
disclose a system in which additional fuel is injected to increase
temperature for regeneration.
In the above systems, however, the performance of the engine may be
adversely affected by changing certain engine parameters for the
purpose of increasing the exhaust temperature. For example,
increasing the amount of fuel to the engine may increase exhaust
temperature, but also increases fuel usage. Varying injection and
ignition timing affects engine performance, for example by causing
the engine to knock.
The present invention is directed to overcoming one or more of the
problems as set forth above.
SUMMARY OF THE INVENTION
In one aspect of the present invention a method for initiating
regeneration of a particulate matter (PM) filter in an exhaust
system in an internal combustion engine is disclosed. The method
includes the steps of determining a change in pressure of exhaust
gases passing through the PM filter, and responsively varying an
opening of an intake valve in fluid communication with a combustion
chamber.
In another aspect of the present invention an apparatus for
initiating regeneration of a particulate matter (PM) filter in an
EGR system in an internal combustion engine having a combustion
chamber and an intake valve in fluid communication thereof is
disclosed. The apparatus includes means for determining a change in
pressure of exhaust gases passing through the PM filter, and a
controller for responsively varying an opening of the intake
valve.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic representation of an internal combustion
engine having an intake and an exhaust system;
FIG. 2 is a diagrammatic and cross-sectional illustration of a
portion of an internal combustion engine;
FIG. 3 is a schematic representation of an internal combustion
engine having an alternate embodiment exhaust system;
FIG. 4 is a graph illustrating control of an intake valve in an
internal combustion engine;
FIG. 5 is a flow diagram illustrating a preferred method of the
present invention; and
FIG. 6 is a flow diagram illustrating an alternate method of the
present invention.
DETAILED DESCRIPTION
Referring to the drawings and the appended claims, a method and
apparatus 100 for initiating regeneration of a particulate matter
(PM) filter 106 in an exhaust system 103 in an internal combustion
engine 102 is disclosed. The exhaust system 103 may include an
exhaust gas recirculation (EGR) system 104.
FIG. 1 illustrates a schematic representation of an internal
combustion engine 102 having an intake passageway 108 and an
exhaust passageway 110. An engine block 202 provides housing for at
least one cylinder 112. FIG. 1 depicts six cylinders 112. However,
any number of cylinders 112 could be used, for example, three, six,
eight, ten, twelve, or any other number. The intake passageway 108
provides an intake path for each cylinder 112 for air, recirculated
exhaust gases, or a combination thereof. The exhaust passageway 110
provides an exhaust path for each cylinder 112 for exhaust
gases.
In the embodiment shown in FIG. 1, a two-stage turbocharger system
114 is illustrated. The turbocharger system 114 includes a first
turbocharger stage 116 having a low pressure turbine 122 and a
first stage compressor 124. The turbocharger system 114 also
includes a second turbocharger stage 118 having a high pressure
turbine 120 and a second stage compressor 126. The two-stage
turbocharger system 114 operates to increase the pressure of the
air and exhaust gases being delivered to the cylinders 112 via the
intake passageway 108, and to maintain a desired air to fuel ratio
during an extended open duration of an intake valve, as is
described in more detail below. It is noted that a two-stage
turbocharger system 114 is not required for operation of the
present invention. Other types of turbocharger systems, such as a
high pressure ratio single-stage turbocharger system, a variable
geometry turbocharger system, and the like, may be used instead.
Furthermore, the present invention may be used with an engine 102
having no turbocharger system at all.
A throttle valve 134, located in the intake passageway 108, may be
used to control the amount of air and recirculated exhaust gases
being delivered to the cylinders 112. The throttle valve 134 is
shown between the second stage compressor 126 and an aftercooler
136. However, the throttle valve 134 may be positioned at any
location along the intake passageway 108. Operation of the throttle
valve 134 is described in more detail below.
The EGR system 104 shown in FIG. 1 is typical of a low pressure EGR
system in an internal combustion engine. Variations of the EGR
system 104 may be equally used with the present invention.
Furthermore, other types of EGR systems, for example, by-pass,
venturi, piston-pumped, peak clipping, and back pressure, could be
used as well. In addition, the exhaust system 103 may have no EGR
system 104 at all.
An oxidation catalyst 128 receives exhaust gases from the low
pressure turbine 122. The oxidation catalyst 128 may also be
coupled with a De-NO.sub.x catalyst to further reduce NO.sub.x
emissions. A PM filter 106 receives exhaust gases from the
oxidation catalyst 128. Although the oxidation catalyst 128 and the
PM filter 106 are shown as separate items, they may alternatively
be combined into one package.
Some of the exhaust gases are delivered out the exhaust from the PM
filter 106. However, a portion of exhaust gases are rerouted to the
intake passageway 108 through an EGR cooler 130, through an EGR
valve 132, and through the turbocharger system 114.
FIG. 3 shows a variation of the EGR system 104 of FIG. 1. In FIG.
3, some of the exhaust gases are routed from the low pressure
turbine 122, through the oxidation catalyst 128, and through the PM
filter 106. However, a portion of exhaust gases are rerouted to the
intake passageway 108 from the low pressure turbine 122, i.e.,
before entering the oxidation catalyst 128, through an additional
PM filter 302, then through the EGR cooler 130, EGR valve 132, and
the turbocharger system 114. The additional PM filter 302 may be
smaller in size than the PM filter 106 in the main exhaust stream
since only a portion of the exhaust gases need be filtered. In
addition, by installing the additional PM filter 302 in the return
path of the EGR system 104, the packaging and routing of the filter
302 and the associated input and output ductwork becomes more
compact and manageable around the vicinity of the engine 102.
Referring to FIG. 2, a diagrammatic and cross-sectional
illustration of a portion of an internal combustion engine 102 is
shown. A cylinder head 211 is connected to the engine block 202.
The cylinder head 211 houses one or more cylinders 112, for example
six cylinders as shown in FIGS. 1 and 3. For purposes of
illustration, FIG. 2 is described below with reference to one
cylinder 112.
The cylinder 112 contains a piston 212 slidably movable in the
cylinder 112. A crankshaft 213 is rotatably disposed within the
engine block 202. A connecting rod 215 couples the piston 212 to
the crankshaft 213 so that sliding motion of the piston 212 within
the cylinder 112 results in rotation of the crankshaft 213.
Similarly, rotation of the crankshaft 213 results in a sliding
motion of the piston 212. For example, an uppermost position of the
piston 212 in the cylinder 112 corresponds to a top dead center
position of the crankshaft 213, and a lowermost position of the
piston 212 in the cylinder 112 corresponds to a bottom dead center
position of the crankshaft 213.
As one skilled in the art will recognize, the piston 212 in a
conventional, four-stroke engine cycle reciprocates between the
uppermost position and the lowermost position during a combustion
(or expansion) stroke, an exhaust stroke, and intake stroke, and a
compression stroke. Meanwhile, the crankshaft 213 rotates from the
top dead center position to the bottom dead center position during
the combustion stroke, from the bottom dead center to the top dead
center during the exhaust stroke, from top dead center to bottom
dead center during the intake stroke, and from bottom dead center
to top dead center during the compression stroke. Then, the
four-stroke cycle begins again. Each piston stroke correlates to
about 180.degree. of crankshaft rotation, or crank angle. Thus, the
combustion stroke may begin at about 0.degree. crank angle, the
exhaust stroke at about 180.degree., the intake stroke at about
360.degree., and the compression stroke at about 540.degree..
The cylinder 112 includes at least one intake port 208 and at least
one exhaust port 210, each opening to a combustion chamber 206. The
intake port 208 is coupled to the intake passageway 108 and the
exhaust port 210 is coupled to the exhaust passageway 110. The
intake port 208 is opened and closed by an intake valve assembly
214, and the exhaust port 210 is opened and closed by an exhaust
valve assembly 216. The intake valve assembly 214 includes, for
example, an intake valve 218 having a head 220 at a first end 222,
with the head 220 being sized and arranged to selectively close the
intake port 208. A second end 224 of the intake valve 218 is
connected to a rocker arm 226 or any other conventional
valve-actuating mechanism. The intake valve 218 is movable between
a first position permitting flow from the intake port 208 to enter
the cylinder 112 and a second position substantially blocking flow
from the intake port 208 to the cylinder 112. Preferably, a spring
228 is disposed about the intake valve 218 to bias the intake valve
218 to the second, closed position.
A camshaft 232 carrying a cam 234 with one or more lobes 236 is
arranged to operate the intake valve assembly 214 cyclically based
on the configuration of the cam 234, the lobes 236, and the
rotation of the camshaft 232 to achieve a desired intake valve
timing. The exhaust valve assembly 216 is configured in a manner
similar to the intake valve assembly 214 and is preferably operated
by one of the lobes 236 of the cam 234. In one embodiment, the
intake lobe 236 is configured to operate the intake valve 218 in a
conventional Otto or diesel cycle, whereby the intake valve 218
moves to the second, closed position from between about 10.degree.
before bottom dead center of the intake stroke and about 10.degree.
after bottom dead center of the compression stroke. Alternatively,
the intake valve assembly 214 and/or the exhaust valve assembly 216
may be operated hydraulically, pneumatically, electronically, or by
any combination of mechanics, hydraulics, pneumatics, and/or
electronics.
In the preferred embodiment, the intake valve assembly 214 includes
a variable intake valve closing mechanism 238 structured and
arranged to selectively interrupt cyclical movement of and extend
the closing timing of the intake valve 218. The variable intake
valve closing mechanism 238 may be operated hydraulically,
pneumatically, electronically, mechanically, or any combination
thereof. For example, the variable intake valve closing mechanism
238 may be selectively operated to supply hydraulic fluid, for
example, at a low pressure or a high pressure, in a manner to
resist closing of the intake valve 218 by the bias of the spring
228. That is, after the intake valve 218 is lifted, i.e., opened,
by the cam 234, and when the cam 234 is no longer holding the
intake valve 218 open, the hydraulic fluid may hold the intake
valve 218 open for a desired period. The desired period may change
depending on the desired performance of the engine 102. Thus, the
variable intake valve closing mechanism 238 enables the engine 102
to operate under a conventional Otto or diesel cycle or under a
variable late-closing Miller cycle. In alternative embodiments, the
intake valve 218 may be controlled by a camless system (not shown),
such as an electrohydraulic system, as is well known in the
art.
As shown in FIG. 4, the intake valve 218 may begin to open at about
360.degree. crank angle, that is, when the crankshaft 213 is at or
near a top dead center position of an intake stroke 406. The
closing of the intake valve 218 may be selectively varied from
about 540.degree. crank angle, that is, when the crankshaft 213 is
at or near a bottom dead center position of a compression stroke
407, to about 650.degree. crank angle, that is, about 70.degree.
before top center of the combustion stroke. Thus, the intake valve
218 may be held open for a majority portion of the compression
stroke 407, that is, for the first half of the compression stroke
407 and a portion of the second half of the compression stroke
407.
A controller 244 may be electrically connected to the variable
intake valve closing mechanism 238. Preferably, the controller 244
is configured to control operation of the variable intake valve
closing mechanism 238 based on one or more engine conditions, for
example, engine speed, load, pressure, and/or temperature in order
to achieve a desired engine performance. It should be appreciated
that the functions of the controller 244 may be performed by a
single controller or by a plurality of controllers.
Referring back to FIG. 1, a means 138 for determining pressure
within the PM filter 106 is shown. In the preferred embodiment, the
means 138 for determining pressure includes a pressure sensor 140.
However, other alternate means 138 may be employed. For example,
the pressure of the exhaust gases in the PM filter 106 may be
estimated from a model based on one or more parameters associated
with the engine 102. Parameters may include, but are not limited
to, engine load, engine speed, temperature, fuel usage, and the
like.
A means 142 for determining flow of exhaust gases through the PM
filter 106 may be used. Preferably, the means 142 for determining
flow of exhaust gases includes a flow sensor 144. The flow sensor
144 may be used alone to determine pressure in the PM filter 106
based on changes in flow of exhaust gases, or may be used in
conjunction with the pressure sensor 140 to provide more accurate
pressure change determinations.
Referring again to FIG. 3, an additional means 304 for determining
pressure, preferably an additional pressure sensor 306, is located
with the additional PM filter 302. In like manner, an additional
means 308 for determining flow of exhaust gases may be used to help
determine the pressure within the additional PM filter 302. The
additional means 308 for determining flow of exhaust gases
preferably includes an additional flow sensor 310. Use of the
additional flow sensor 310 and additional pressure sensor 306 is
typically similar to that described with respect to the pressure
and flow sensors 140,144 of FIG. 1.
Industrial Applicability
Operation of the present invention may be described with reference
to the flow diagram of FIG. 5.
In a first control block 502, a change in pressure of exhaust gases
passing through the PM filter 106 is determined. The change in
pressure results from an accumulation of particulate matter, thus
indicating a need to regenerate the PM filter 106, i.e., burn away
the accumulation of particulate matter. For example, as particulate
matter accumulates, pressure in the PM filter increases.
In a first decision block 504, it is determined if the change in
pressure has exceeded a predetermined threshold, i.e., an allowable
maximum pressure level. If the predetermined threshold has not been
exceeded, then monitoring of the pressure continues. However, if
the predetermined pressure level threshold has been exceeded,
control proceeds to a second control block 506.
In the second control block 506, the open duration of the intake
valve 218 is extended, preferably into the compression stroke 407,
as indicated by the graph of FIG. 4. During this time period,
compression of the cylinder 112 takes place. Since the intake valve
218 is open for a portion of the compression stroke, a small
quantity of air or recirculated exhaust gases is forced out of the
cylinder 112 by the pressure of compression. For example, the air
may reduce from 80% to 70% in mass flow rate. The reduction in air,
with the same amount of fuel, results in a richer mixture which,
when combusted, generates a similar amount of heat, but at a higher
temperature. Thus, the exhaust gases which pass from the cylinder
112 are at a higher temperature.
Preferably, the increase in temperature of the exhaust gases is
enough to initiate regeneration in the PM filter 106. However, if
it is determined, in a second decision block 508, that regeneration
has not been initiated, control proceeds to a third control block
510. In the third control block 510, the throttle valve 134 in the
intake passageway 108 is actuated by the controller 244 to
partially close, thus further reducing the amount of air entering
the cylinder 112. This further reduction of air results in a still
richer fuel/air mixture, which in turn results in even higher
exhaust gas temperatures. The throttle valve 134 is controlled in
cooperation with the extended open duration of the intake valve 218
to reach the exhaust temperature needed to initiate regeneration of
the PM filter 106.
It is noted that other methods for increasing the exhaust
temperature may be used in cooperation with extending the open
duration of the intake valve 218. For example, variable geometry
turbochargers, smart wastegates, injection timing of the fuel, and
the like, may be used.
In a third decision block 512, it is determined if the change in
pressure of the PM filter 106 has decreased to below the
predetermined threshold. If yes, then engine operation returns to
normal.
FIG. 6 is a flow diagram which illustrates a slight variation from
the embodiment of FIG. 5.
In a first control block 602, the pressure of the exhaust gases
passing through the PM filter 106 is determined.
In a first decision block 604, it is determined if the change in
pressure has exceeded a first predetermined threshold. If yes,
control proceeds to a second control block 606, in which the open
duration of the intake valve 218 is extended.
In a second decision block 608, it is determined if regeneration is
initiated. If no, control proceeds to a third control block 610, in
which the throttle valve 134 is controllably actuated.
In a third decision block 612, it is determined if the change in
pressure has decreased to less than a second predetermined
threshold. If yes, operations return to normal.
If the first and second predetermined thresholds are the same, then
the embodiment of FIG. 6 is identical to the embodiment of FIG. 5.
However, it may be preferred to set the second predetermined
threshold to a value less than the first predetermined threshold to
establish a range for activation and deactivation of the present
invention.
It is noted that the additional PM filter 302 shown in FIG. 3 would
benefit from the same methods described above with respect to the
original PM filter 106 of both FIGS. 1 and 3.
Other aspects can be obtained from a study of the drawings, the
disclosure, and the appended claims.
* * * * *